Wednesday, January 24, 2018

Wavin Insights: Sewer blockages caused by tree root growth

Tree roots growing inside sewer pipes are not an uncommon problem. They thrive on oxygen, so they will not grow in pipes that are filled with water. Rather, they will propagate in a warm, moist and nutrient-rich environment. The subsequent sewer damage can be quite staggering, not to mention costly. Wavin examines the causes and effects of tree root growth in sewage systems, and what we can do to prevent damage in our underground infrastructure. 

Root growth in sewers – causes and effects

Tree root penetration in sewer systems cause significant pipe damage. Municipalities, businesses and homeowners alike have experienced serious headaches from sewer problems caused by roots. Roots that grow rapidly can leave infrastructure fully unusable – and the associated repair or replacement costs are substantial. It is estimated that more than 50% of all sewer blockages are due to tree root invasion. A recent geostatistical study conducted in Bogotá (Colombia)confirmed what most biologists and underground engineers have found – "that larger trees are prone to cause more pipe damage; therefore tree-pipe distance is a relevant parameter control for reducing potential deterioration.” Interestingly enough, the study found that cumulative precipitation and pipe length showed no effect on observed root intrusion events.” It is clear that some pipe materials are more resistant to root intrusion than others. 

Some facts:

  • Old pipes with joints, shallow or small pipes are more prone to root growth
  • Less joints in sewer lines (and longer lines) means less possibility for root growth
  • Large, fast-growing trees are the biggest contributors to root growth in sewer pipes
  • Sewer pipes made from materials like clay, brick or concrete will deteriorate over time, causing them to separate and crack from ground shifting/heaving and erosion.Roots from trees growing near the sewer lines can gain entry through cracks in the sewer pipes. As these roots expand, they can build up immense pressure and this can be powerful enough to break open even the tightest and most dense pipe connections. Sewer lines are usually laid in depths of 2 meters or more.
  • Tree roots that penetrate at that depth are called tree “anchor roots” and can surround intact pipes without causing any problems. Damage occurs only when there is a crack or opening in the pipe, thus allowing the roots to creep in and thrive.
    Feeder roots” are the fine, hair-like fibrous roots that are usually located within the first meter of the soil.
  • A cracked sewer line causes water and sewage to leak and air to escape into the soil – creating the perfect mix of oxygen, water and nutrients for tree roots to thrive. This causes the anchor root to grow very fine feeder roots which penetrate the cracked pipe and cause blockage.
  • According to IKT (Institute for Underground Infrastructure), a root can grow in the pipe connection for more than two years, before it penetrates the pipe’s seal.

Sewer lines and pipe materials

What do you do when your sewer gets clogged by tree roots? Wavin looks to Patrick de Beerengineer with PipeVision for some answers.

Wavin: How often are sewer blockages causes by root ingrowth?

Patrick de Beer:That depends on how old a sewer line is. This mostly happens with older sewers that weren't installed properly in the first place.

Wavin: What are the most probable causes when a sewer is overgrown with roots?

Patrick de Beer: When inlets have been created in concrete sewer lines, connections that are not closed off – both are by far the most common cause for root ingrowth. When a sewer line is properly installed root ingrowth is very rare.


Wavin: So, can we conclude it doesn't happen often in newer sewer lines?

Patrick de Beer:  It doesn't happen often in PVC sewer pipes as PVC connections are often strong and impenetrable. PVC pipe usually need less joints. Also the joints on PVC pipes are tightly fitted and thus leakage is less likely. We do see it often in (older) concrete sewer pipes..

Wavin:  How do you tackle root growth in sewers?

Patrick de Beer:  We use a root cutter or special sewer cleaning nozzle like a Warthog, to clean out the roots. But root cutting is like pruning, the roots will always grow back. This is a temporary solution. It's better to opt for a sewer renovation, where part of the pipes is replaced with newer material. Another option is relining the pipe.

The costs

Pipe collapse repair costs can be greater than those associated with new construction. And when you’re dealing with the repair of main drains and sewers, particularly as a result of root tree growth, this tends to be quite expensive. These insidious tree roots can cause sewer damage which, in turn, can flood streets and buildings– much to the dismay of the municipality, building- and home owner. Costs escalate and sewer service replacement/repair can run in the thousands of euros. A research study published in The Journal of Infrastructure Systems, titled Tree Root Intrusion in Sewer Systems: Review of Extent and Costs, found that “the costs associated with root removal may be one-sixth the cost of pipe replacement/renewal due to tree root growth.” So, what are some of the measures that we can take to prevent tree root growth in our sewer systems?

Tree root growth prevention 

Soil solutions, thoughtful tree landscaping, and properly installed sewer lines with durable piping material are the three key measures to prevent tree root growth in sewers.
  • Soil solutions: IKT recommends the implementation of passive and active protective measures. Passive measures would involve, for example, installing liquid soil in the trench because it prevents root growth. More active measure would include soil aeration, planting pits and root trenches.

Image: Soil aeration (Image via

  • Sewer-safe trees:  Something to bear in mind is that you can control where you plant your trees and what type of trees you plant. Always limit the amount of trees you plant in close proximity to your sewer line. It is advisable to plant smaller trees (with shallow root structures) near your sewer line. Some evergreens, like Cypress, and a few fruit trees (like cherry, plum, and peach) are less likely to damage sewer pipes. Keep the larger trees as far away from the sewer as possible.Some of the notorious fast-growing trees to avoid planting near your sewer line are: maple, poplar, birch, willow, elm, ash cottonwood, and Russian olive.

Image: Japanese Cherry Tree - this is a "sewer-sage" tree  (Image via Wikimedia Commons)

  • Plastic PVC pipes – a sustainable optionRoots travel in search of water. If left untreated, tree roots may completely block the flow of waste water inside the sewer pipe. But, if a sewer line is properly sealed and in good condition, it will likely not be susceptible to root invasion. Root-resistent pipe connections like jacket pipes (which protect the pipe) or laying down panels and foil in the trenches – to keep pipes and roots away from each other. Additionally, the pipe material plays a very significant role in root penetration. Plastic PVC pipes are durable and sustainable, which is why Wavin’s piping solutions are such a popular choice for sewage and drainage systems. They’re lightweight, easy to install and maintain, and – above all – they don’t crack. When sewer pipes crack, the tree roots will invade the pipe and grow… and grow.


As we always say, it is better to be safe than sorry. So, if you can, try to be proactive with your soil management and tree planting. As for your sewer system, there will be tell-tale signs if there’s a problem. Basement flooding, gurgling sounds in your toilet, regular plumbing stoppages – these are indications of a problem that may be root-related. If this happens, call your favorite plumbing professional to diagnose the problem and provide you with options to resolve it.


For more information on Wavin’s plastic piping solutions for sewage and drainage, go to our Knowledge Center, where you will find the latest news and reference cases.

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